Task tray notifier

We are interested in? having a small notification application built for the purpose of sending alerts to Windows users. The system should have two parts: 1) A? server-side application that? queries a SQL Server database at set intervals and retrieves a list of alerts for different users. The server app will also need to report to the database when? a user signs in or? signs out. 2) A task tray application that sits on a user's PC and receives messages from the server app. When a message is received, a balloon? should pop up containing the message, and? a sound should be played, to get the user's attention. It is important? that this notification system not place a heavy load on the web server.? If possible,? the server application should? "push"? alerts to? the user, rather than? the users constantly querying the server, even when they have no messages. Thank you